This proposal consists of two parts. In the first, we propose to study the physiology and pharmacology of synaptic receptors of goldfish ganglion cells, both for enzymatically dissociated cells in culture and for cells in slices of intact retina. Recordings from ganglion cells will be made with patch-clamp techniques in both the whole-cell and isolated patch modes. We plan (1), a characterization of excitatory amino acid receptors on isolated ganglion cells; (2), further study of the effects of inhibitory amino acids, including a study of the nature of GABA desensitization, an investigation of the mechanism of strychnine block for GABA and glycine, and an explanation of the noise spectrum for glycine whole-cell currents in terms of single-channel responses; (3), a survey of the effects of peptides and other putative neurotransmitters on dissociated ganglion cells; and (4), the development of a system for making recordings from ganglion cells in slices of goldfish retina. In the second part of this proposal, we propose to use microelectrode recording, external perfusion, and microspectrophotometry to elucidate the mechanism of dark adaptation in vertebrate rods and cones. These experiments are designed to test the "equivalent background hypothesis" of dark adaptation at the level of single photoreceptors. We also plan to investigate a possible role for intracellular calcium concentration in controlling sensitivity during recovery after pigment bleaching.